09a: Vision Flashcards by Nuna H

List the various segments of photoreceptor and function/characteristic of each segment.

Outer (photosensitive)
Inner (contains mitochondria and nucleus)
Synaptic ending (communicates with retina)

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T/F: Rods and cones are identical in structure, despite difference in function.

False - outer segments vary

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(Rods/cones) are very sensitive to light, capable of responding to single photon.

Rods

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Scotopic vision is (day/night/color) vision and carried out most effectively by (rods/cones).

Night; rods

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Photopic vision is (day/night/color) vision and carried out most effectively by (rods/cones).

Day; cones

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(Rods/cones) contains rhodopsin, which is comprised of: (star the light-catching part)

Both;

Opsin (integral membrane protein)
11-cis retinal (chromophore)*

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To increase packing density of (X), (rods/cones) have:

X = rhodopsin

Rods: membranous disks on outer segment
Cones: invaginations/sacs on outer segment

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Which key part of rods/cones is derivative of Vitamin (X).

X = A

11-cis retinal (chromophore of rhodopsin)

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Absorption of (X) number of photon(s) isomerizes (Y) to (Z).

X = 1
Y = 11-cis retinal
Z = all-trans retinal

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When is rhodopsin “bleached”?

All-trans retinal detaches from opsin

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T/F: when rhodopsin is bleached, it can no longer absorb visible light.

True

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First step of phototransduction cascade.

Activated rhodopsin (all-trans retinal) activates transducin (G-protein)

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Transducin is a(n) (X) which, when activated by (Y), leads to:

X = G-protein
Y = Rhodopsin (active)

Activation of PDE

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Transducin activates (X), which causes (Y), thus (increasing/decreasing) (Z).

X = PDE
Y = rapid hydrolysis of cytosolic cGMP
Decreasing;
Z = cGMP levels

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In darkness, (low/high) levels of (X) keeps constant (influx/efflux) of (Y) ion(s) in (inner/outer) segment of photoreceptors.

High; 
X = cGMP;
Influx of (Y=) Na and Ca in outer segment;
Efflux of (Y=) K from inner segment

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Typical resting Vm of photoreceptor.

-35 mV

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The photoreceptor is more (de/hyper)-polarized than typical neuron, which keeps (X) channels (open/closed) in synaptic ending. This leads to continuous (Y).

Depolarized;
X = Ca
Open
Y = release of glutamate

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In (presence/absence) of light, there is constant release of which AA?

Absence;

Glutamate

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(Rods/cones) generate action potentials.

Neither! Photoreceptors don’t generate action potentials

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(Rods/cones) generate receptor potential that’s graded in response to (X).

Both;

X = intensity of light

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The signal from photoreceptors first passes to (X) cells and then to (Y) cells.

X = bipolar
Y = retinal ganglion

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List the classes of bipolar cells.

H-bipolars (off-center)

2. D-bipolars (on-center)

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H-bipolar cells express (X) receptors, so light causes them to (de/hyper)-polarize.

X = ionotropic glutamate

Hyperpolarize

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D-bipolar cells express (X) receptors, so light causes them to (de/hyper)-polarize.

X = metabotropic glutamate

Depolarize

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(D/H)-bipolar cells generate action potential.

Neither!

The reason (photoreceptors/bipolars/retinal ganglions) don't generate AP is because distance of propagation of electrical signals is small enough for efficient electronic spread.

Bipolar cells

(H/D)-bipolar cells establish an excitatory synapse with subsequent (X) cells.

H: (X=) off-center retinal ganglion cells D: (X=) on-center retinal ganglion cells

(On/off)-center retinal ganglion cells generate action potentials.

Both

Light causes (X) response in H-bipolar cells and then (Y) response in (Z) cells.

``` X = hyperpolarization Y = inhibition of action potentials Z = off-center retinal ganglion ```

Light causes (X) response in D-bipolar cells and then (Y) response in (Z) cells.

``` X = depolarization Y = activation of AP Z = on-center retinal ganglion ```

The optic nerve is formed from axons of (X) cells.

X = retinal ganglion

Which cells in retina are involved in lateral interactions?

1. Horizontal cells | 2. Amacrine cells

Horizontal cells in retina present extensive (Y) processes that intermingle with (Z).

``` Y = dendritic Z = processes of photoreceptors and bipolar cells ```

Stimulation of horizontal cells causes them to (stimulate/inhibit) neighboring synapses.

Inhibit

Amacrine cells in retina present extensive (Y) processes that intermingle with (Z).

``` Y = dendritic Y = processes of bipolar cells and ganglion cells ```

Cones contain the same (photopigment/chromophore), but three different forms of (photopigments/chromophores), linked to (same/different) (X).

Chromophore; Photopigments X = the same chromophore

Blue cones preferentially absorb light in (X) range wavelength.

X = short (peak 420 nm)

Green cones preferentially absorb light in (X) range wavelength.

X = medium (peak 530 nm)

Red cones preferentially absorb light in (X) range wavelength.

X = long (peak 560 nm)

(Rods/cones) have more direct path to Ganglion cells.

Cones

(Rods/cones) have higher degree of convergence and, thus, (high/low) spatial resolution.

Rods; low

Receptive field center receives (direct/indirect) input from:

Direct; photoreceptor

Receptive field surround receives (direct/indirect) input from:

Indirect; horizontal cells

Response to light in field center is (same/opposite) of response to light in the surround.

Opposite

On-center (X) cells respond to (light/dark) in (center/surround) of receptive field.

X = retinal ganglion; Light; Center

Off-center (X) cells respond to (light/dark) in (center/surround) of receptive field.

X = retinal ganglion; Dark; Center

(On/off)-center ganglion cells are very responsive to changes in illumination that include both center & surround.

Neither! Responsive to changes in contrast between center/surround

At t0, the center and surround of receptive field are same shade of grey. At t1, the center goes a shade of darker grey. How do on/off-center retinal ganglion cells respond?

On-center: less AP fired | Off-center: more AP fired

At t0, the center and surround of receptive field are same shade of grey. At t1, the center goes a shade of darker grey. How do on/off-center (or D/H-) bipolar cells respond?

D (on-center): hyperpolarize | H (off-center): depolarize

At t0, the center is a shade of darker grey than the surround. At t1, the center turns the same shade of grey as the surround. How do on/off-center retinal ganglion cells respond?

On-center: more AP fired | Off-center: less AP fired

At t0, the center is a shade of darker grey than the surround. At t1, the center turns the same shade of grey as the surround. How do on/off-center (or D/H-) bipolar cells respond?

D (on-center): depolarize | H (off-center): hyperpolarize

In dark adaptation of retina, (X) cells (increase/decrease) their sensitivity.

X = photoreceptor; | Increase

In light adaptation of retina, (X) cells (increase/decrease) their sensitivity.

X = photoreceptor; | Decrease

Light adaptation occurs via (X) feedback since bright light effect of (increase/decrease) in (X) will cause (increase/decrease) production of (Y).

X = Ca; Decrease (in cytoplasmic Ca); Increase; Y = cGMP

Light adaptation: (high/low) cytoplasmic (X) causes (increase/decrease) affinity of (Y) to (Z) channels.

``` Low; X = Ca; Increase; Y = cGMP Z = Na/Ca channels ```

Each retina's visual field can be divided into (X) and (Y) divisions.

``` X = temporal Y = nasal ```

Left eye receives information about (left/right) visual field.

Both!

The temporal division of the right retina receives information from which visual field?

Left visual field

The nasal division of the left retina receives information from which visual field?

Left visual field

The nasal division of the right retina receives information from which visual field?

Right visual field

Right optic nerve contains information from (right/left) eye and (right/left) visual fields.

Right; both

At the optic chasm, (X) retinal fibers decussate, but (Y) retinal fibers do not.

``` X = nasal; Y = temporal ```

Right optic tract fibers contain information from (right/left) eye and (right/left) visual fields.

Both eyes; | Left (contralateral) visual field

Info from right visual field will travel in (right/left) optic nerve and (right/left) optic tract.

Both optic nerves; | Left optic tract

Damage to region of optic chasm would result in vision loss from which part of

Nasal retina

Vision pathway: At (X), a small fraction of (Y) fibers will synapse in (Z) to provide light/dark information for regulating circadian rhythms.

``` X = optic chiasm; Y = retinal ganglion cell Z = suprachiasmatic nucleus (of hypothalamus) ```

Majority of fibers in optic tract will synapse on cells in:

LGN (thalamus)

Minority of fibers in optic tract will pass through/around (X) to synapse on:

X = LGN; 1. Pretectum nuclei OR 2. Superior colliculus nuclei

Visual input to pretectum is for (conscious/unconscious) (X).

Unconscious; | X = pupillary reflex and lens control

Visual input to superior colliculus is for (conscious/unconscious) (X).

Unconscious; | X = orienting movement of head/eyes

Our conscious perception of visual world: visual input from retinal ganglion cell projection to (X), then (Y).

``` X = LGN Y = primary visual cortex ```

Right LGN receives information from (right/left) eye and (right/left) visual field.

Both eyes; | Left visual field

LGN has (X) number of layers that can be divided into which group(s)?

X = 6 1. Magnocellular (inner two layers) 2. Parvocellular (outer four layers)

T/F: LGN cells have center/surround excitatory/inhibitory organization.

True

(X) cells of LGN have large cell bodies and (small/large) receptive fields. (Y) cells of LGN have small cell bodies and (small/large) receptive fields.

X = M (magnocellular) Large; Y = P (parvocellular) Small

(X) cells of LGN have fast and transient responses. This contributes to their high sensitivity to:

X = M Contrast

(X) cells of LGN have slow conduction velocity and (low/high) sensitivity to changes in contrast.

X = P | Low

(X) cells of LGN carry more information about details than (Y) cells of LGN.

``` X = P Y = M ```

(X) cells of LGN carry information about color.

X = P (only)

(X) cells of LGN provide info with high temporal resolution.

X = M

(X) cells of LGN provide info with high spatial resolution.

X = P

Which LGN layers contain maps of contralateral visual field? And ipsilateral visual field?

Each layer contains complete map of CONTRALATERAL visual field

Which LGN layers receives input from contralateral eye? And ipsilateral eye?

Ipsilateral: 5, 3, 2 Contralateral: 6, 4, 1

Main projection from LGN is to:

Striate cortex (aka V1 or primary visual cortex)

The striate cortex has (X) number of layers and projects to:

X = 6; | V2-V5 and other extrastriate visual areas

There's greater representation of (X) retina regions than (Y) retina regions in striate cortex.

``` X = fovea/parafoveal Y = peripheral ```

Visual input from the L/R eyes begins to be (separated/combined) in the cells of (X).

Combined; | X = striate cortex

(LGN/striate cortex) is organized into groups of columns, formally called (X) columns. Cells in adjacent columns have difference in:

``` Striate cortex; X = orientation columns Orientation preference (by 10o) ```